Hmmm i charge my batteries at no more thane 3 Amp.
3000 Nihm batteries charging at 3.5 Amp should get you around 8 Min. Run time.
If your looking for longer run time.
Get a lipo or these batteries by Duratrax
http://www3.towerhobbies.com/cgi-bin...&I=LXNCR1&P=ML
I use those in my truck's and i love theme.